Development of a thin film transistor using an organic semiconductor has gradually become active since the latter half of 1980s. In recent years, the basic performance of the thin film transistor using the organic semiconductor has exceeded the properties of a thin film transistor of amorphous silicon. The use of an organic material as a semiconductor layer in a thin film device is attractive because the organic material can be easily processed and often has a high affinity for a plastic substrate on which a thin film field effect transistor (FET) is formed. Examples of the researches on organic semiconductors reported heretofore include: acenes such as pentacene and tetracene disclosed in Japanese Patent Application Laid-Open No. H05-55568; phthalocyanines including lead phthalocyanine, low-molecular weight compounds such as perylene and tetracarboxylic acid derivatives thereof disclosed in Japanese Patent Application Laid-Open No. H05-190877; aromatic oligomers typified by thiophene hexamers called α-thienyl or sexthiophene and high molecular compounds such as polythiophene, polythienylenevinylene, and poly-p-phenylene vinylene disclosed in Japanese Patent Application Laid-Open No. H05-190877. Most of those compounds are described in Advanced Material, 2002, vol. 14, no. 2, p. 99-117.
The properties such as nonlinear optical properties, conductivity, and semiconductivity necessary for using those compounds as semiconductor layers to obtain devices greatly depend on not only the purity of the material but also the crystallinity and orientation of the material. A compound with an extended n conjugated system is typically insoluble or hardly soluble in a solvent. For example, a pentacene thin film is produced by means of vacuum vapor deposition because pentacene has high crystallinity and is insoluble in a solvent. The pentacene thin film produced by means of vacuum vapor deposition is known to exhibit a high field effect mobility, but involves a problem in that the pentacene thin film is unstable in the air, is susceptible to oxidation, and is thus apt to deteriorate.
On the other hand, an organic semiconductor using as an organic semiconductor film a π conjugated system polymer is excellent in processability. For example, the organic semiconductor can easily be formed into a thin film by means of solution coating or the like. Therefore, the applied development of the organic semiconductor has been pursued (“Japanese Journal of Applied Physics”, The Japan Society of Applied Physics, 1991, vol. 30, p. 596-598). The arrangement state of molecular chains is known to largely affect the electrical conductivity of the π conjugated system polymer. Similarly, it has been reported that the field effect mobility of a π conjugated system polymer field effect transistor greatly depends on the arrangement state of molecular chains in a semiconductor layer (“Nature”, Nature Publishing Group, 1999, vol. 401, p. 685-687). However, the arrangement of molecular chains in the π conjugated system polymer is performed during the period from the application of a solution to the drying of the solution, so the arrangement state of the molecular chains may vary to a large extent owing to a change in environment and a difference in application method.
In addition, an FET has been reported, which uses a film obtained by: forming a thin film of a soluble precursor of pentacene by application; and transforming the precursor into pentacene through heat treatment (J. Appl. Phys., vol. 79, 1996, p. 2136). In this case, the transformation of the precursor into pentacene involves the necessity for high temperature treatment or for removal of an eliminated component having a large mass under reduced pressure.
Furthermore, it has been reported that tetrabenzoporphyrin obtained by heating, at 210° C. or higher, porphyrin in which a bulky bicyclo[2.2.2]octadiene skeleton is condensed can be used as an organic semiconductor (The Chemical Society of Japan 81st spring annual meeting, 2002 conference proceedings II, p. 990 (2F9-14), Japanese Patent Application Laid-Open No. 2003-304014, and Japanese Patent Application Laid-Open No. 2004-6750). However, it can never be said that the carrier mobilities described in those publications are excellent. That is, in order to provide sufficient properties for an organic semiconductor, further investigation into the attainment of an optimum crystalline orientation is considered to be necessary for the purpose of increasing a carrier mobility.
As described above, for a field effect transistor using an organic semiconductor compound, a semiconductor layer having crystallinity and orientation has been formed by undergoing a process such as vacuum film formation. For example, an acene is a representative example of the organic semiconductor compound. However, there has involved a problem in that the acene is susceptible to oxidation, and is thus apt to deteriorate. In addition, a film obtained by a simple method using application method faces the task of establishing an approach to forming a film excellent in both of orientation and crystallinity.